‘Let’s face it’: McEnroe calls out Serena

The tennis world was rocked by the high drama of Serena Williams’ ‘never seen before’ collapse. Picture: Michael Klein

DESPITE Serena Williams' insistence her final set fade-out was a result of Karolina Pliskova's incredible play, tennis legend John McEnroe believes the greatest female player of all time choked.

Williams exited in the quarter-finals despite leading 5-1 in the third set and while noting she was impeded by an ankle turn, McEnroe said the pressure of winning another grand slam - which would equal Margaret Court's record of 24 - also played a part.

"As you get older, you realise you have less opportunity maybe to pull this off. So you put more pressure on yourself," McEnroe said.

"It looked like at the end, the pressure, which is very rare - I didn't think I would be saying this - but the pressure of the moment got to her a bit."

"(It's) a little bit of choking, yeah," he added, when asked if it was a choke. "Let's face it, they're all human beings."

Williams offered a different explanation for failing to convert three match point opportunities.

"I literally did everything I could on those match points," she said. "It's not like - yeah, I can't say that I choked on those match points. She literally played her best tennis ever on those shots."

McEnroe was also critical of Japan star Kei Nishikori's retirement in his quarter against Novak Djokovic.

Kei Nishikori has come under fire after retiring in his quarter-final.

Nishikori withdrew down 6-1 4-1 and drew little sympathy because of his failure to put away early round opponent's more efficiently and record as a serial quitter.

"The guy looked absolutely spent in the warm-up," McEnroe said.

"Some of this was Kei's fault, he should have put away Karlovic, he should have won his first round match against a qualifier more easily, he didn't, it caught up with him.

"It is sort of like a middleweight playing heavyweights. At a certain point he gives in mentally.

"That is why he hired Chang. Michael wouldn't do that. You could see Michael's dismay, the coach, in the coach's box, 'Why do you have to stop playing?'

"That is not in (Chang's) DNA. He's trying to get that more into Kei, but Kei is more conservative.

"Some guys and girls have higher thresholds for pain than others and they can go out there and compete at a higher level for longer. He is not one of them."

Rafael Nadal will take on Stafano Tsitsipas in the semi-finals. Picture: Michael Klein

Day 11 preview

Rafael Nadal has blasted through the draw without dropping a set, but Stefanos Tsitsipas could be a tougher proposition after he pulled off the win of his life to knock out Roger Federer in four sets in the last 16.

The Spanish second seed, who plays the night match, is wary of the new Greek star, who he called "one of the best players in the world".

But he also declared his own time was not yet up as he chases an 18th Grand Slam title.

"They can wait a little bit," said Nadal of the new kids on the block. "But looks like they don't want to."

Seeded 14, Tsitsipas has plenty of respect for the world number two but is also surging with confidence at his best Grand Slam ever.

"I feel like I can do something good against him," said the 20-year-old.

The second men's semi-final, between six-time winner Novak Djokovic and Lucas Pouille, who is in his first last four match at a major, will be played on Friday.

Danielle Collins is making noise. (AAP Image/Ritchie Tongo)

In the women's singles, two-time Wimbledon champion and eighth seed Kvitova faces tournament surprise package Danielle Collins, who stunned world No.2 Angelique Kerber on her way to her first grand slam semi.

The unheralded American has adopted an aggressive approach during her campaign and is looking forward to meeting Kvitova, who beat her at the warm-up Sydney International in three tight sets.

"She's an incredible champion, has gone through a lot," Collins said, referring to the knife attack on Kvitova in December 2016 that almost derailed her career.

"We had a really great battle a couple weeks ago, one of the best matches I've played and I didn't even win. So I'm very familiar with her."

In the second women's semi-final, US Open champion Naomi Osaka takes on dangerous Czech Karolina Pliskova, who sensationally bounced back from 5-1 down in the third set to knock out Serena Williams in the last eight.

The Japanese fourth seed is looking to win back-to-back grand slam titles and is expecting a testing encounter from the never-say-die seventh seed.

"She's really tough to play. Like, I can barely read her serve, so it's very difficult for me," she said.